The invention relates to steam generation apparatus and particularly to heat recovery steam generation apparatus. Gas turbines are widely used to generate electrical power particularly to provide stand by or peak power supplements and for unattended service in remote locations. Their thermal efficiency is relatively low because of high exit gas temperatures and extremely high excess air percentages. In many cases, the thermal efficiency of a gas turbine plant can be improved by adding heat recovery equipment. More particularly, there are often economic benefits from adding either a fired or unfired steam generator to an existing gas turbine installation.
Unfired boilers have been used mainly for the production of process steam. In some applications they have been used for power generation or space heating,
The conventional approach to utilizing the gas turbine exit gas has been to connect the exhaust of the gas turbine by means of a diffuser to a heat recovery steam generator. Such diffusers have a relatively long and expensive duct from the turbine to the heat recovery steam generator. While the present invention has particular application to heat recovery steam generators it will be understood by those skilled in the art to have application to other vapor generation apparatus as well as to any application where it is desired to provide a duct for a fluid, in a small space, between a high velocity application and a low velocity application. Obviously the gas turbine is one such high velocity application and the heat recovery steam generator is one such low velocity application.
The prior art includes ladder vanes that are provided to deflect gas streams for various uses includes directing gases over heat exchange surfaces. The prior art includes the use of pressure gradient arrays including the use of a plurality of pipes arranged to deflect an air stream by positioning the pipes with the respective axes thereof in a common plane which is oblique to the initial direction of gas flow. The prior art also includes the use of pipes which are spaced at non-uniform distances.